Battery jumper cables are commonly used to jump start automobiles and other vehicles having batteries that are discharged. A booster battery, typically one on another vehicle, is positioned in the vicinity of the discharged battery to allow use of the jumper cables to bypass the discharged battery and start the disabled vehicle. Once the vehicle has been started, its battery is charged to its normal voltage level by a generator or alternator carried on the vehicle.
Among the disadvantages of jump starting vehicles in this manner is the need for another vehicle having a properly charged battery. If the disabled vehicle is in an isolated location or if another vehicle is not readily available for some other reason, this procedure can involve considerable delay. Even then, it is necessary for space to be available close enough to the discharged battery for the second vehicle to be positioned where the cables can be extended between the two batteries. It is not unusual for the cables to be attached improperly to the battery terminals, and such improper connections can cause damage to the battery or electrical system of one or both vehicles.
In recognition of these and other problems, self-contained jump start units have been developed. On these devices, a booster battery is contained inside of a housing and is equipped with cables and battery clamps that are connected to the battery terminals, either permanently, removably, or through a switch. A vehicle with a discharged battery can be started by connecting the clamps of the jump start unit to the battery terminals of the disabled vehicle and using the booster battery to bypass the discharged battery.
In recent years, portable jump start units that can be carried by hand from place to place have been available in addition to larger wheel mounted units. The portable device is only slightly larger than a modern automotive battery and can be conveniently carried on a vehicle so that it is available in the event of a problem with the normal vehicle battery. It is also easy to position the jump start unit close to the discharged battery in situations where limited space is available. An example of a portable jump start unit is disclosed in U.S. Pat. No. 5,589,292.
A problem with the portable jump start units that have been proposed in the past is the way in which the battery clamps are stored when they are not being used. The clamps are often connected permanently to the battery terminals, and they are always "live" (although units with switches have been available). Therefore, the clamps should be stored so that they are protected from being inadvertently contacted by other objects or by the other clamp of the jump start unit. Units such as that described in U.S. Pat. No. 5,589,292 not only fail to secure the clamps in a secure and stable position when they are not being used, but they actually allow the clamps to turn about a round pin against which the jaws of the clamp are closed.
Another problem has been that the clamp handles or other parts of the clamps can project (due to rotation or otherwise) beyond the plane of the front or back of the housing. Consequently, if the unit is lying on a conductive surface, the only thing preventing a short circuit is insulation on the clamps, which can be worn away or otherwise lose its insulative effect.
Battery chargers are usually provided with the jump starter so that the booster battery can be maintained in a fully charged condition. The battery charger normally has a body containing a transformer that can be plugged into an electrical outlet. A plug carried on a cord extending from the charger body can be inserted into a jack on the jump starter housing in order to make charging current available to the battery contained in the housing.
If the battery charger is to be available when needed, it must be stored with the jump start unit. Portable units that have been available in the past and have provided for storage of the battery charger have stored the charger either in a simple cavity, where it can fall out, or loosely in a storage compartment, where it can rattle around unduly and fall out when the compartment is opened.